Vision Research 51 (2011) 1829–1834

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Vision Research

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Resolution of static and dynamic stimuli in the peripheral visual field

Peter Lewis a,⇑, Robert Rosén b, Peter Unsbo b, Jörgen Gustafsson a

a Section of Optometry and Vision Science, Linnæus University, Kalmar, Swedenb Biomedical & X-Ray Physics, KTH, Royal Institute of Technology, Stockholm, Sweden

a r t i c l e i n f o

Article history:Received 19 November 2010Received in revised form 31 May 2011Available online 21 June 2011

Keywords:Visual acuityResolution acuityDynamic visual acuity (DVA)Peripheral visionDrifting Gabor

0042-6989/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.visres.2011.06.011

⇑ Corresponding author. Fax: +46 480 446262.E-mail address: peter.lewis@lnu.se (P. Lewis).

a b s t r a c t

In a clinical setting, emphasis is given to foveal visual function, and tests generally only utilize static stim-uli. In this study, we measured static (SVA) and dynamic visual acuity (DVA) in the central and peripheralvisual field on healthy, young emmetropic subjects using stationary and drifting Gabor patches. Therewere no differences between SVA and DVA in the peripheral visual field; however, SVA was superiorto DVA in the fovea for both velocities tested. In addition, there was a clear naso-temporal asymmetryfor both SVA and DVA for isoeccentric locations in the visual field beyond 10� eccentricity. The lack ofdifference in visual acuity between static and dynamic stimuli found in this study may reflect the useof drift-motion as opposed to displacement motion used in previous studies.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction Glansholm, 1975; Lundström et al., 2007; Millodot et al., 1975;

The visual world in which we live contains both static anddynamic components. As such, the visual system has developedto respond to a wide variety of stimuli.

The most widely used measure of visual function is the mea-surement of visual acuity, which is the ability of the eye to resolvedetail in an image. The conventional method of measuring visualacuity employs stationary letters or symbols (optotypes) of highcontrast viewed at a specific testing distance. In a clinical settingemphasis is concentrated on foveal visual acuity; in fact, it is gen-erally only foveal acuity that is measured for example whenassessing suitability for holding a motor vehicle driving license inmany countries (Bohensky, Charlton, Odell, & Keeffe, 2008).

Resolution thresholds of the eye are limited by the optics of theeye, the spacing of the photoreceptors and the spacing of ganglioncells in the retina (Anderson, Mullen, & Hess, 1991; Atchison,Schmid, & Pritchard, 2006; Banks, Sekuler, & Anderson, 1991;Campbell & Green, 1965; Ennis & Johnson, 2002; Frisén & Glans-holm, 1975; Lundström et al., 2007; Millodot, Johnson, Lamont, &Leibowitz, 1975; Popovic & Sjöstrand, 2005; Thibos, Cheney, &Walsh, 1987; Wang, Thibos, & Bradley, 1997; Williams, Artal, Nav-arro, McMahon, & Brainard, 1996).

In the fovea, spatial resolution is predominantly optically lim-ited, in contrast to the periphery (beyond 10�) where spacing ofmidget ganglion cells is the major factor determining the limitsof resolution (Anderson, Wilkinson, & Thibos, 1992; Banks et al.,1991; Campbell & Green, 1965; Curcio & Allen, 1990; Frisén &

ll rights reserved.

Popovic & Sjöstrand, 2001, 2005; Thibos et al., 1987).Static visual acuity (SVA) declines rapidly with increasing

eccentricity from the fovea in a symmetrical fashion in both thenasal and temporal visual fields out to an eccentricity of approxi-mately 10� (Anderson, Zlatkova, & Demirel, 2002; Frisén & Glans-holm, 1975; Thibos et al., 1987). Beyond this, SVA is better in thetemporal visual field than in the nasal visual field. These differ-ences have been attributed to lateral asymmetry of retinal ganglioncells beyond the optic nerve head (Anderson et al., 2002; Fahle &Schmid, 1988; Frisén, 1987; Frisén & Glansholm, 1975; Rovamo,Virsu, Laurinen, & Hyvärinen, 1982).

When relative motion exists between an observer and an objectof interest, there will also be a corresponding movement of the im-age of the object on the observer’s retina in relation to the fovea. Inorder to maintain good image clarity, the eye must track and focusthe moving object so that the image is correctly imaged upon thefovea. This requires a pursuit tracking movement of the eye. Theterm ‘‘dynamic visual acuity’’ (DVA) was first proposed by Ludvighand Miller (1958) to describe the ability of the eye to resolve stim-uli, moving in relation to an observer.

It is accepted that foveal DVA diminishes as the angular velocityof a stimulus increases (Bex, Dakin, & Simmers, 2003; Brown,1972a, 1972b; Burg, 1965; Chung & Bedell, 2003; Demer, 1995;Demer & Amjadi, 1993; Fergenson & Suzansky, 1973; Ludvigh &Miller, 1958; Murphy, 1978; Westheimer & McKee, 1975). In addi-tion to velocity dependence, other factors affecting DVA have alsobeen widely studied. These include illumination, pupil diameter,contrast, gender, age, alcohol, marijuana, and training effects.Further information regarding these factors can be found in the re-view articles by Miller and Ludvigh (1962) and Morrison (1980), aswell as in Dwight Holland’s (2001) doctorial thesis.

Fig. 1. Experimental setup with seven CRT-screens. The subjects fixated on thecentral screen (FOV) with their right eye, whilst the left eye was occluded with apatch. Negative eccentricity (�10� to �30�) represents the nasal visual field of theright eye, whereas positive eccentricity (+10� to +30�) represents the temporalvisual field.

1830 P. Lewis et al. / Vision Research 51 (2011) 1829–1834

Most studies of DVA have examined stimuli moving at relativelylarge angular velocities and those utilizing eye-tracking devicesshow that inadequate pursuit eye-movements is the key factorresulting in decreased DVA (Barmack, 1970; Brown, 1972a; Demer& Amjadi, 1993; Reading, 1972a). This ‘‘mismatch’’ between eye-movements and stimulus velocity causes retinal image slip, whichresults in movement of the image relative to the fovea.

The majority of researchers have used Landolt C stimuli (Emoto,2010; Haarmeier & Thier, 1999; Long & Johnson, 1996; Ludvigh &Miller, 1958; Miller, 1958; Miller & Ludvigh, 1962; Peters &Bloomberg, 2005; Reading, 1972b; Smither & Kennedy, 2010;Ueda, Nawa, Yukawa, Taketani, & Hara, 2006) although there area few exceptions. Behar, Kimball, and Anderson (1976) and Burg(Burg, 1966; Burg & Hulbert, 1961) used Bausch & Lomb checker-board targets. Demer and Amjadi (1993) used Sloan optotypes.Geer and Robertson (1993) and Schneiders et al. (2010) both uti-lized Landolt E stimuli. Gratings in various forms have been usedby McKee and Nakayama (1984) and Aznar-Casanova, Quevedo,and Sinnett (2005).

Differences in DVA between different stimuli have beenreported, whereby the major factor affecting performance is theorientation of stimulus in relation to the direction of movement(Prestrude, 1987).

The type of stimulus also dictates the type of movement thatcan be presented; displacement motion or drifting motion. Duringdisplacement motion, the stimulus changes position in the visualfield over time. For drifting motion the stimulus remains at thesame location whilst every element of the pattern undergoes atemporal phase change; giving the impression of movement withinan aperture (Aznar-Casanova et al., 2005). Gratings and Gaborpatches can be utilized to show both displacement and driftmotion, whereas other stimuli can only be presented using dis-placement movement.

The disadvantage of displacement motion is that stimuli do notremain at the same location and consequently, the retinal area stim-ulated varies depending on both stimulus velocity and duration.

It is important to note that subjects in the majority of previousstudies had to follow moving stimuli, and that the associatedreduction in DVA occurred when ocular pursuit movements wereno longer able to maintain the stimulus on the fovea.

Two noteworthy studies conducted Brown (1972a, 1972b) exam-ined DVA in the peripheral visual field in the absence of voluntaryeye-movements. DVA using displacement motion and under steadyfixation, deteriorated when relative movement exceeded approxi-mately 2–4�/s. These results have also been repeated by Demerand Amjadi (1993) and Aznar-Casanova et al. (2005). Aznar-Casa-nova et al. (2005) used an exposure duration of 700 ms, whereas De-mer and Amjadi (1993) used 16 s, and Brown (1972a, 1972b),400 ms.

In the case of drifting motion, deterioration in DVA begins fromvelocities as low as 0.5�/s (Aznar-Casanova et al., 2005) showingthat the mechanisms behind impaired performance are not identi-cal for displacement and drifting motion.

The aim of this study was to measure SVA and DVA at specificlocations in the horizontal visual field on healthy, young emmetro-pic subjects. The stimuli, namely stationary and drifting Gaborpatches, were chosen as these allowed well-defined retinal locationsto be tested irrespective of stimulus velocity.

2. Methods

2.1. Apparatus

Stimuli were generated on a PC microcomputer (MSI K9A2 Plat-inum motherboard) running Windows XP and MATLAB� software

(MathWorks, Natick, MA) with extensions supplied with the Psy-chophysics Toolbox (Brainard, 1997). Four ATI Radeon™ HD 4350graphic cards were used to drive 8 IBM (G96) 190 0 CRT monitorswith a resolution of 1280 � 1024 (dot pitch 0.25 mm) with arefresh rate of 85 Hz and with a mean luminance of 43–45.3 cd/m2. An i1Display 2 colorimeter from X-Rite was used to calibrateand correct the luminance and gamma function of the monitors.One of the eight monitors was used solely as a slave monitor tocontrol stimulus presentation within Matlab on the remainingmonitors.

The remaining seven monitors were situated at a distance of3.0 m from the subject thus forming an arc with a constant radiusof 3.0 m (see Fig. 1). A forehead-rest was utilized to maintain thisobservation distance without restricting the horizontal visual field.

2.2. Stimulus generation

Test stimuli consisted of circular Gabor patches (i.e., rx = ry)with a visible angular diameter of 2� (r = 0.5�). Only high contrast(98% or greater) stimuli were used in this study.

The general formula for the Gabor stimuli was as follows:

Lðx; yÞ ¼ Lm½1þ sinð2pxfs þ /Þ� � exp½�ðx2 þ y2Þ=ð2r2Þ�

Dynamic stimuli were identical to static stimuli in every respectexcept that the sine wave function was temporally modulated, cre-ating an associated translation of the grating within the Gaussianenvelope. Two velocities were adopted: 1�/s and 2�/s and the direc-tion of movement were always laterally, from right to left (creatingsimilar motion as if reading a text from left to right). The choice oftested velocities was based upon previous studies (Demer, 1995;Demer & Amjadi, 1993; Westheimer & McKee, 1975) showingmarked deterioration of visual acuity for stimuli drifting at veloci-ties greater than approximately 2�/s.

The Gabor patches were orientated obliquely; leaning either±45� from the vertical in order to reduce the superiority of acuityfor gratings orientated vertically or horizontally (Berkley, Kitterle,& Watkins, 1975; Campbell, Kulikowski, & Levinson, 1966; West-heimer, 2003) and the possible influence of off-axis astigmatism

Fig. 2. Mean static and dynamic acuity for all subjects. Error bars denote ± SEM.

P. Lewis et al. / Vision Research 51 (2011) 1829–1834 1831

in the peripheral visual field (Gustafsson, Terenius, Buchheister, &Unsbo, 2001; Rempt, Hoogerheide, & Hoogenboom, 1976).

2.3. Experimental method

Resolution thresholds were determined for 0, 1 and 2�/s at thefollowing retinal locations: in the fovea, 10�, 20� and 30�; bothnasally [�] and temporally [+].

2.3.1. SubjectsA total of 10 naïve subjects participated (mean age 25.5 years,

ranging from 19 to 38 years). All were emmetropic (refrac-tion 6 ±0.50D and astigmatism < �0.50DC) and had unaided fovealvisual acuities of 6/6 or better and no known ocular disease. Sub-jects viewed the fixation screen with their right eye while wearinga patch over their left eye. No optical correction was utilized fov-eally or eccentrically.

Written informed consent was obtained from each subject afterthe nature and purpose of the experiment had been explained. Thetenets of the Declaration of Helsinki were followed.

2.3.2. ProcedureSubjects were seated at a distance of 3.0 m from the seven mon-

itors and instructed to observe a fixation target (in the form of amagnified asterisk ‘‘�’’) on the centermost monitor for all measure-ments except for those in the fovea where the fixation target wasreplaced by the stimulus.

Each measurement trial was initiated by the subject pressing akey on a modified numerical keypad. A tone preceded each stimu-lus presentation. Following a delay of 500 ms, the stimulusappeared on the monitor being tested and remained visible for aduration of 300 ms; this to avoid saccadic re-fixation eye-movements. All responses were recorded using the modifiednumerical keypad.

The thresholds were determined by a two-alternative forced-choice (2AFC) procedure in which the subjects had to determinethe orientation of the grating. The threshold value correspondedto the stimulus strength estimated giving 75% correct response rateand the psychometric function was assumed to be logistic. Anadaptive Bayesian algorithm proposed by Kontsevich and Tyler(1999) was used to calculate a probability density function forthe threshold, with the expectation value taken as the measure-ment. After 31 trials the probability density function in generalassumed a normal distribution, with an average standard deviationof 0.085 log MAR.

Resolution thresholds were obtained at one retinal eccentricityat a time so that visual attention was concentrated on the correctlocation. The order of testing followed a predetermined randomprotocol in order to reduce possible training effects and subjectswere given the opportunity to take breaks between trials.

2.3.3. Control experimentsTwo control experiments were performed in order to determine

the effect of exposure duration and to ascertain the highest spatialfrequency at which the subject could still perceive motion of Gaborstimuli moving at 1 and 2�/s.

In the first control experiment, which in effect followed thesame procedure as in the main experiment, resolution thresholdswere measured using exposure durations of 300, 700 and1500 ms at 10� and 20� in the nasal visual field of three subjectswho had participated in the previous experiment. The average ofthree measurements was recorded for each eccentricity andvelocity.

In the second control experiment, exposure duration was main-tained at 300 ms whilst spatial frequency was altered, howeverthe aim of this experiment was to see the highest spatial frequency

whereby the subject could still perceive movement of the Gaborpatch. The same two velocities were used as in the main experiment,namely 1 and 2�/s. One experienced subject (PL) participated in thisexperiment. The average of three series consisting of 45 trials wasrecorded for both velocities and for eccentricities of 10� and 20� inthe nasal visual field.

3. Results

The main result of this study is that there were no differences be-tween SVA, DVA1�/s and DVA2�/s in the periphery for the mean of thepopulation tested. This was confirmed by two-way repeated mea-sures ANOVA (p > 0.05/3) with adjustment for multiple comparisons(Bonferroni) at all eccentricities. The exception was the fovea, whereSVA was better than both DVA1�/s (p < 0.05) and DVA2�/s (p < 0.01).There was however no difference between DVA1�/s and DVA2�/s inthe fovea.

The mean visual acuity ± one standard error of the mean (SEM)for all subjects under static and dynamic conditions is shown inFig. 2.

One-way repeated-measures ANOVA followed by Bonferronimultiple comparisons showed significantly differences betweenthe nasal and temporal visual fields for eccentricities of 20� and30� for SVA, DVA1�/s and DVA2�/s. There was however no naso-temporal asymmetry between SVA, DVA1�/s and DVA2�/s at aneccentricity of 10�.

The mean of all values for SVA and DVA for all subjects are pre-sented below in Table 1.

3.1. Results of control experiments

Results of the first control experiment (see Fig. 3), in whichexposure duration was altered, showed no significant differencein visual acuity between 300, 700 and 1500 ms for stimuli movingat a velocity of 1�/s at two tested locations in the nasal visual field.

Thresholds for perceiving movement of 1 and 2�/s wereobtained on one subject (see Fig. 4). The highest spatial frequencyin which movement was still perceived at 1�/s was 0.57 log MAR at10 N and 0.60 log MAR at 20 N. For a velocity of 2�/s the thresholdwere 0.93 log MAR and 0.77 log MAR respectively for 10� and 20�in the nasal visual field. This means the subject was able to discernthat stimuli were in motion up to, or even above the limit of reso-lution for an exposure duration of 300 ms.

4. Discussion

This study on a population of healthy young emmetropesshowed no difference between static (SVA) and dynamic visualacuity (DVA) at eccentricities of ±10�, 20� and 30�. Foveal

Table 1Mean static and dynamic log MAR acuities (±1SEM) for all subjects.

(Nasal) Eccentricity (Temporal)

�30 �20 �10 FOV +10 +20 +30

SVA 1.13 ± 0.03 0.89 ± 0.06 0.53 ± 0.04 �0.04 ± 0.01 0.56 ± 0.04 0.66 ± 0.03 0.83 ± 0.02DVA1�/s 1.12 ± 0.03 0.86 ± 0.03 0.60 ± 0.02 0.06 ± 0.03 0.50 ± 0.05 0.68 ± 0.02 0.80 ± 0.02DVA2�/s 1.13 ± 0.03 0.91 ± 0.03 0.50 ± 0.02 0.12 ± 0.04 0.57 ± 0.02 0.72 ± 0.02 0.81 ± 0.02

Fig. 3. The effect of exposure duration on visual acuity at 10� (squares ‘‘j’’) and 20�(triangles ‘‘N’’) in the nasal visual field. Error bars represent the standard error of themean (SEM) of three repeated measurements on three subjects.

Fig. 4. Motion discrimination thresholds as a function of velocity at 10� and 20� inthe nasal visual field on one experienced subject (PL). Filled diamonds ‘‘�’’ andsquares ‘‘j’’ represent the average of three measurements at 10� and 20�respectively in the nasal visual field (error bars represent the standard deviationof these three measurements). Open symbols represent previously measured visualacuity at the same locations and velocities.

1832 P. Lewis et al. / Vision Research 51 (2011) 1829–1834

resolution was best for SVA and decreased with increasing stimu-lus velocity. This is in accordance with previous studies that havemeasured DVA under conditions of steady fixation (Aznar-Casa-nova et al., 2005; Brown, 1972b; Demer & Amjadi, 1993; Macedo,Crossland, & Rubin, 2008; Nes, 1968). Aznar-Casanova et al.(2005) showed that visual acuity measured using drifting gratingsdecreased with increasing stimulus velocity. They found that in thecase of drift motion, foveal visual acuity began to deteriorate fromas little as 0.5�/s, which supports the findings in this study. Thevisual system on the other hand has been shown to tolerate retinalmotion of 2–4�/s when viewing stimuli moving within the visualfield, also termed ‘‘displacement motion’’ (Demer & Amjadi, 1993).

In contrast to earlier studies of DVA in which displacementmotion was employed (Brown, 1972a, 1972b; Burg, 1965; Geer &Robertson, 1993; Ludvigh & Miller, 1958; Macedo, Crossland, & Ru-bin, 2011; Miller, 1958; Peters & Bloomberg, 2005; Reading,1972b; Ueda et al., 2006) we have endeavored to measure visual

acuity at specific locations in the visual field by using a drifting Ga-bor-patch of a fixed angular size. The area stimulated in this studywas limited to 2� irrespective of stimulus velocity, whereas forexample, in Brown’s study (1972a) the stimuli traversed a greaterarea of the retina as stimulus velocity increased. This is one possi-ble explanation for the perceived improvement in peripheral visualacuity for relatively low stimulus velocities (under 10�/s) found intheir studies; namely, that the retinal area tested enlarged as stim-ulus velocity increased.

Similar results have been obtained by Macedo et al. (2008) fornon-crowded stimuli whereby visual acuity improved slightly withincreased retinal slip. In contrast, peripheral visual acuity deterio-rated substantially for crowded stimuli. Above a certain threshold,a corresponding retinal image slip results in a deterioration in acu-ity. Demer and Amjadi (1993) reported that foveal visual acuitydeteriorated rapidly for retinal image motion in the order of2–4�/s (measured by displacement motion). Aznar-Casanovaet al. (2005) also determined that for low velocity stimuli (0–5�/s) visual acuity deteriorated at least two and a half times fasterfor displacement motion than for drifting motion, as used in thisstudy.

The results of this study confirm previous studies, which evalu-ated various measures of peripheral visual function (resolution,detection, contrast thresholds, temporal resolution, etc) in that aclear naso-temporal asymmetry for SVA exists. SVA is better inthe temporal visual field than in the nasal visual field, as can beseen in Fig. 2. Curcio and Allen (1990) showed that the basis of thisnaso-temporal asymmetry is anatomical; cell counts show higherdensity in the nasal retina than in the temporal retina. Ganglioncell receptor fields also show same asymmetry.

The observed reduction in acuity may, in part, also reflect thenaso-temporal asymmetry of optical aberrations in the periphery,whereby both lower-order and higher-order aberrations are morepronounced in the nasal visual field (Atchison, Pritchard, White,& Griffiths, 2005; Gustafsson et al., 2001).

However other research (Rosén, Lundström, & Unsbo, 2011)show no difference in resolution thresholds for high-contrast staticand dynamic stimuli after correction of optical defocus. It would beinteresting to study the effect of correction on low-contrast DVA inthe future.

To our knowledge, no studies have evaluated DVA at multipleretinal locations along the horizontal visual field. This study showsa clear naso-temporal asymmetry for both SVA and DVA based onthe averaged results of 10 subjects.

The average difference in SVA and DVA between the nasal andtemporal visual fields at 30� was approximately 0.3 log MAR, andat 20�, approximately 0.2 log MAR. There was no apparent differ-ence at 10� other than for a stimulus velocity of 1�/s whereby theaverage threshold was 0.1 log MAR lower in the temporal visualfield than in the nasal visual field.

5. Conclusions

This study on a population of young emmetropes showed, forisoeccentric locations in the visual field beyond 10� eccentricity,

P. Lewis et al. / Vision Research 51 (2011) 1829–1834 1833

a clear naso-temporal asymmetry for both SVA and DVA, measuredusing high-contrast stimuli. There were no differences betweenSVA and DVA in the peripheral visual field, however foveal SVAwas superior to DVA for both velocities tested.

The lack of difference in visual acuity between static anddynamic stimuli found in this study may reflect the use of drift-motion as opposed to displacement motion used in previous stud-ies. The specific area tested also remained constant irrespective ofstimulus velocity.

These findings are possibly more pertinent for patients withcentral visual field loss (CFL) in that, such patients are restrictedto using a limited peripheral retinal location when observing bothstatic and dynamic stimuli.

Acknowledgments

This research was supported by the Swedish Optometry Branchand Faculty of Natural Sciences and Technology, Linnaeus Univer-sity, Kalmar.

We would also like to acknowledge Karthikeyan Baskaran forhis assistance in both control experiments and suggestions onthe manuscript.

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